Strain gages are commonly used to detect stresses in materials, changes in pressure and temperature, etc. Typically, strain gages employ one or more piezoresistive elements or piezoresistors which experience a change in resistance when subjected to strain induced by physical and/or chemical stimuli. The piezoresistive elements found in a conventional strain gage are usually formed of several loops of fine wire or a special foil composition. In use, the gage is bonded to the surface of the object to be analyzed. When the object is deformed in response to particular stimuli, the piezoresistive elements of the gage are strained which alters the resistance of the piezoresistive elements. The change in resistance is measured and then is correlated to the level of strain experienced by the object.
Recently, micro-electromechanical sensors have been developed that arc manufactured by semiconductor microelectronic processing and precision etching technologies. These sensors can be employed for measuring parameters such as pressure, acoustic vibrations, inertia (acceleration, vibration, shock), gas concentration, temperature etc. Such sensors typically employ micromechanical elements (membranes, cantilever beams, microbridges, tethered proof masses, etc.) which are perturbed by physical and/or chemical stimuli, with the magnitude of the perturbation being related to the magnitude of the physical or chemical stimuli. Typically, piezoresistors are positioned on the micromechanical element at high-stress locations of the micromechanical element (for example, at the edge of a membrane). The sensitivity of such sensors is proportional to the piezoresistive gage factor of the piezoresistors, defined as: GF=.DELTA.R/R.epsilon., the relative change in resistance .DELTA.R/R with strain .epsilon..
Silicon is a common material for forming the piezoresistors in micro-electromechanical sensors and has a gage factor that is suitable for various applications. However, in some instances, a higher gage factor is desirable so that the sensitivity of the sensor incorporating the piezoresistor can be increased, or alternatively, the micromechanical element on which the piezoresistor is positioned, can be stiffened for increased mechanical strength without reducing the sensitivity of the sensor. Attempts have been made to produce piezoresistors with higher gage factors than silicon, however, such attempts have not produced significantly higher gage factors with consistant piezoresistive properties.